The OFDM [Orthogonal Frequency-Division Multiplexing] technique has been known in the telecommunications field for many years; according to this technique, information is transferred from a transmitter to a receiver by modulating a plurality of frequency-adjacent carriers (forming a single frequency band), which are referred to by those skilled in the art as “sub-carriers”.
More recently, it has been thought of implementing the OFDM technique through non-adjacent sub-carriers, so as to form at least two sub-bands more or less distant from each other. In this manner, the frequencies between the two sub-bands can be used for other communications; such implementations can be grouped under the name “NC-OFDM technique” [Non-Contiguous OFDM].
In most (theoretical and practical) cases, these techniques are implemented by using a fixed band (in the case of the most traditional implementations of the OFDM technique) or multiple fixed bands (in “non-contiguous” implementations of the OFDM technique).
Unlike the NC-OFDM technique, document WO2008/089402 describes a solution based on the OFDM technique which relates to the IEEE 802.11 standard family and which uses dynamic band allocation; according to this solution, the transmitter generates an OFDM signal having a variable band unknown a priori to the receiver; for the receiver to correctly receive said signal, an additional field that signals carrier usage by the transmitter during the transmission has been added into the PLCP [Physical Layer Convergence Protocol] header of the PPDU [Physical layer Protocol Data Unit] container of the IEEE 802.11 protocol; with 48 sub-carriers available, for each of them it is signalled if it is in use and according to which modulation scheme it is being modulated.